Nanocrystals (also referred to as quantum dots) are often used as catalysts for many catalytic reactions due to their high surface area to volume ratio. Reactions where nanocrystal catalysts can be used include methanation, oxygen reduction, methanol reduction, steam reforming, water-gas shift reactions, NOx oxidation, SOx oxidation, disproportionation of hydrogen peroxide, alkylation, catalytic cracking, naphtha reforming, ammonia or acid production, and other catalytic reactions. The electronic properties of nanocrystals are typically different than the properties of the bulk material. The performance and efficacy of a catalyst for a specific chemical reaction depends on these electronic properties. In particular, the Fermi level of a nanocrystal catalyst plays a crucial role in catalytic performance.
To find an appropriate catalyst, one must find a nanocrystal with the desired energy levels that are applicable for the products and reactants of the catalytic reaction. However, finding a nanocrystal catalyst with the desired energy levels can be a daunting task. Furthermore, a nanocrystal catalyst with the desired electronic properties may be costly; therefore it would be advantageous to be able to alter a less expensive or more readily available nanocrystal to have the desired energy levels. Electronic energy levels, including the Fermi level and the d-band centroid and width, of a nanocrystal are determined primarily by the nanocrystal's elemental composition, size, and morphology. By changing the composition, size, and/or morphology of the nanocrystal, one may be able to tune the energy levels indirectly to match the desired energy levels. However, these changes are non-trivial or impossible. Moreover, it is typically difficult to precisely determine how the energy levels will be altered from indirect changes to the composition, size, and/or morphology of the catalyst.
Accordingly, there is a need to develop a method of modifying catalytic behavior of nanocrystals by proximity of other nanocrystals to improve catalytic performance, such as increased energy efficiency and lifetime of catalytic systems, reduced cost, and reduced susceptibility to poisoning.